Make sure your device is at least 70% charged to avoid complications during the process.

Section 2: Procedure

Open your preferred file manager and mount the system partition as
read-write in stead of read only. Grant superuser access when it
prompts.

Go to the system folder present in the root of file system. i.e the path- /system

Now open the file “build.prop” in any Text Editor. For Root Explorer users, long click on “build.prop”
file and tap on “Open with Text Editor”. (Before editing this file, for
a safety, copy this file to the external memory card and save as a
backup.)

Now add the following line to this file at the end:

qemu.hw.mainkeys=0

Save and Exit.

Now reboot your device.

See Below Video Tutorial on how to enable onscreen Keys using Rom toolbox Lite